What Are Blood Oxygen Levels?

Blood oxygen levels can also be measured using an instrument known as a pulse oximeter.

Blood oxygen level measures the amount of oxygen carried by red blood cells, which is essential for giving the body's cells the energy they need to work.

Oxygen levels can be measured with a pulse oximeter, often placed on a finger or ear, that can measure oxygen saturation (SpO2) peripherally in the body. Usually, this is the percentage of hemoglobin molecules in red blood cells that have oxygen molecules attached in circulation. This is typically after the heart has pumped blood to the lungs to pick up oxygen, which is then sent to the rest of the body. The probe shines a light through the skin and measures how red the blood appears by how the light glows, since oxygen-rich blood is a brighter red. This is the same principle that smart watches use to measure oxygen in the blood.

In a hospital or clinic setting, in addition to using pulse oximetry, a blood test can be done to directly measure the amount of oxygen in the bloodstream. Arterial blood gas (ABG) not only measures oxygen, but also other blood levels, like carbon dioxide and pH, to better help understand a patient's status in many clinical situations, from heart and lung breathing issues, to acid-base problems in diabetes, infection, and trauma.

For most healthy individuals, a normal blood oxygen level (SpO2) is between 95% and 100%, regardless of age.

Newborns are an exception. For the first few minutes of life, a level between 90% to 95% is considered normal, but it should quickly rise to the 95% to 100% range.

In patients with heart or lung disease, lower SpO2 levels in the 92-94% range may be acceptable.

Normal oxygen level for adults and children

ABG (arterial blood gas) measures levels of oxygen, carbon dioxide, sodium bicarbonate, pH, and sometimes lactic acid and carbon monoxide in blood drawn from an artery. The blood sample is measured by a laboratory machine to give exact readings of oxygen levels.

Pulse oximetry is quite accurate when the SpO2 is greater than 90%, but less so for oxygen levels that are lower.

Hypoxemia is the medical term for having low oxygen levels in your blood (hypo=low + oxy=oxygen + emia=blood). Hypoxia describes low oxygen saturation in the body's tissues. It is defined by an oxygen saturation (SpO2) of less than 90%.

The normal ranges of an ABG test can be seen in the chart below:

The causes of low blood oxygen are many. For normal oxygenation to occur, a person needs to be able to breathe adequately to get oxygen into the lungs. Then, the oxygen needs to be absorbed into the bloodstream. There needs to be enough red blood cells to accept oxygen, and the heart needs to be able to pump blood into the organs of the body.

There are a variety of conditions that can affect the delivery of oxygen from the lungs to the bloodstream, including:

• Weakened breathing effort may slow or stop breathing. This may be a result of a head injury or an alcohol/drug overdose. Sleep apnea can decrease the ability to breathe effectively. In end-stage COPD, patients tire out because the effort of breathing is so hard.
• Lung conditions like asthma, pneumonia, or COPD (Chronic bronchitis, emphysema) make it hard for oxygen to get from the lung tissue into the blood.
• A problem with circulation to the lungs where not enough blood is flowing to pick up oxygen. This might occur in a pulmonary embolus (blood clot in a lung artery) or a pneumothorax (collapsed lung).
• Decreased circulation of tissues in the body can be due to a weak heart that cannot adequately pump blood.
• A problem with red blood cells, like anemia, where there aren't enough red blood cells to carry oxygen.
• Poisoning, like carbon monoxide or cyanide. In both these poisonings, the SpO2 is artificially normal, but an ABG will reveal the hypoxemia.

Hypoxemia is defined by an oxygen saturation (SpO2) of less than 90%. Not having enough blood oxygen levels results in inadequate oxygen supply to the organs and tissues of the body.

When organs don't have enough blood supply, they can stop functioning adequately. A couple of examples include the following:

• When the brain does not get enough oxygen, the patient can become confused, lethargic, and eventually comatose.
• When muscles do not get enough oxygen, they can begin to ache and become painful.

The body tries to compensate and adjust to hypoxemia by increasing the breathing rate and the heart rate. These can only compensate for a short period of time, and for that reason, the cause of hypoxemia needs to be diagnosed and treated relatively quickly.

It is important to treat the underlying condition causing low blood oxygen, but it is more important, at the same time, to provide oxygen to increase levels and allow the body's organs to have enough energy to function. Usually, the goal is to maintain a SpO2 greater than 90%.

In patients with chronic lung or heart disease, home oxygen therapy may be needed.

Prevention or minimizing risk of a variety of illnesses or situations that may result in low blood oxygen levels includes:

• Don't smoke and avoid secondhand smoke, since this can damage both the heart and lungs.
• Stay active with regular exercise to maintain heart and lung function.
• Be proactive in managing existing health conditions, like asthma or heart disease. Take medications as prescribed and see a healthcare provider routinely.
• Prevent infections by getting recommended vaccines, like the influenza, pneumonia, RSV, and COVID.
• Avoid breathing harmful chemicals or pollutants when possible. This includes having carbon monoxide detectors in the home and at work.
• Be cautious at high altitudes by ascending slowly to let your body adjust.

What does the oxygen level in blood tell you?

The oxygen level in your blood (SpO2) provides a measure of how much oxygen is available to be used by the body's tissues and organs.

What should my blood oxygen level be?

Normal oxygen levels (SpO2) are between 95% and 100%, indicating an adequate concentration of oxygen in the bloodstream. Levels below 90% are low (hypoxemia) and may often require treatment.

Is it better to have high or low blood oxygen?

It is always best to have a normal amount of oxygen in the blood. Oxygen levels (SpO2) lower than 90% are not normal and usually need treatment.

What is normal blood oxygen level during sleep?

A normal blood oxygen level (SpO2) while sleeping is generally 95% or higher, though it is common for it to dip slightly below this for short periods. However, SpO2 should not drop below 90% when sleeping.

What blood oxygen level is too low?

A blood oxygen level below 90% is considered too low and is referred to as hypoxemia. Treatment is often needed with supplemental oxygen until the underlying condition is treated or stabilized.

At what oxygen level should you go to the ER?

Low oxygen levels in the blood (SpO2 less than 90%) are not normal and need urgent care. Patients who have shortness of breath, chest pain, or a change in mental status should seek medical care immediately.

In some patients with chronic lung diseases who are on home oxygen, they may be able to adjust their inhaled oxygen percentage under the direction of their healthcare provider. But it is never wrong to seek care.

How can I raise my blood oxygen level?

While you cannot raise your blood oxygen levels on your own, you can minimize your risk of low blood oxygen levels by practicing deep breathing exercises, engaging in regular physical activity, and ensuring proper ventilation or fresh air intake. Avoiding smoking, treating any underlying lung or heart conditions, and using supplemental oxygen (if prescribed by a doctor) are also effective ways to improve oxygen levels.